The present invention is directed generally to reciprocating piston pumps and more particularly to pilot valves used in reciprocating air motors used to drive reciprocating piston pumps.
Reciprocating piston pumps typically include an air-driven motor that converts a steady flow of compressed air into linear reciprocation of an air motor rod using an appropriate reversing valve and a pair of pilot valves, as is known in the art. The air motor rod is then used to drive a linearly reciprocating pump piston that can be configured to pump in both directions using appropriate check valves. These types of linearly reciprocating double-acting piston pumps are commonly used in lubrication dispensing systems to deliver highly viscous lubricants, such as oil or grease.
The reversing valve itself reciprocates to alternatively direct compressed air from a source to opposite sides of an air piston within the air motor to produce the reciprocating action of the pump piston. Reciprocation of the reversing valve is controlled by two pilot valves that engage the air piston at changeover positions to pneumatically change the position of the reversing valve. Engagement of the air piston with one of the pilot valves causes compressed air from the source to be directed to the opposite side of the reversing valve. For example, operation of such a valve combination is described in U.S. Pat. No. 3,943,823 to Tammy.
Compressed air provided to the air motor can include small dust and dirt particles, despite efforts to prevent entry of these particles into the air motor. Prolonged exposure to dust and dirt can degrade performance of moving parts and ultimately lead to failure. Pilot valves include a valve stem that can be subject to cyclic operation upwards of hundreds of actuations per minute. Dust and dirt can cause the valve stems and seals placed around them to prematurely wear out. Replacement of the pilot valves is costly and inconvenient to operators of the air motor. There is, therefore, a continuing need to improve the wear life of moving parts in air motors.